This invention relates to a silver halide photographic material more particularly to one having high contrast.
Photographic image of high contrast is used to form characters and halftone dots in photochemical processes, as well as fineline image in superfine photochemical processes. Certain types of silver halide photographic materials that are used for these purposes are known to be capable of forming photographic image having very high contrast. In the prior art, light-sensitive materials using a silver chlorobromide emulsion that comprises uniformly shaped grains with an average grain size of 0.2 .mu.m and a narrow size distribution and that has a high silver chloride content (of at least 50 mol %) are treated with alkaline hydroquinone developing solutions with low sulfite ion concentrations to produce an image of high contrast, sharpness and resolution, such as a halftone image or fineline image. Silver halide light-sensitive materials used in this method are known as photosensitive materials of the lith type.
The photochemical process includes the step of converting a continuous tone image to a halftone image, namely, the step of converting the change of density in a continuous tone image to a set of halftone dots having areas proportional to the image density. To this end, a document of continuous tone is imaged on the lith-type photosensitive material through a cross-line screen or a contact screen and the material is subsequently developed to form a halftone image. The lith-type photosensitive material used in this step is a silver halide photographic material that contains a silver halide emulsion comprising uniformly sized and shaped fine grains. If this type of photographic material is developed with a common black-and-white developing solution, the resulting dot quality is inferior to that achieved by treatment with a lithographic developing solution which has a very low sulfite ion concentration and which contains hydroquinone as the sole developing agent. However, a lithographic developing solution is so susceptible to autoxidation that its keeping quality is very low. Since controlling the quality of development to be constant is very important for continuous use of developers, much effort is being made to improve the keeping quality of lithographic developing solutions.
With a view to maintaining the keeping quality of lithographic developing solutions, a so-called "two-liquid separated compensation" method is commonly adopted in automatic processors for photochemical processes. This method uses two different replenishers, one being used to compensate for process fatigue (i.e., the deterioration of activity due to development) and the other being used to compensate for aging fatigue (i.e., the deterioration by oxidation due to aging). A problem with this method is that the need to control the balance between the two replenishers for proper replenishment increases the complexity of the apparatus and operations. Further, lithographic development is not capable of rapid access since its induction period (the time required for image to become visible upon development) is long.
Methods are known that are capable of rapid formation of high-contrast image without using lithographic developing solutions. As described in U.S. Pat. No. 2,419,975 and Unexamined Published Japanese Patent Application Nos. 16623/1976 and 20921/1976, etc., these methods are characterized by incorporating hydrazine derivatives in silver halide light-sensitive materials, which hence can be processed with developing solutions that contain sulfite ions at sufficiently enhanced concentrations to insure higher keeping quality. However, the photographic materials processed with these methods have low sensitivity and the halftone image obtained has "black peppers" or sand-like fog in dots and hence is low in quality. In an attempt at solving this problem, various stabilizers or restrainers having hetero atoms have been added but this has not proved to be a complete solution.